1. Field of the Invention
The present invention relates to a laser machining apparatus arranged so as to adjust a laser beam emitted from a laser oscillator in X and Y directions on a workpiece by means of an optical axis adjusting unit comprising two mirrors.
2. Description of Related Art
FIG. 4 is a schematic structural view showing a conventional laser machining apparatus and FIG. 5 is a diagram schematically showing a conventional optical system.
The conventional laser machining apparatus 60 comprises a laser oscillator 1, a total reflection mirror 3, an external optical system 4, a total reflection mirror 5, an optical axis adjusting unit 6, a condenser lens (fθ lens) 8 and a table 10. A laser beam 2 emitted from the center of an opening (emitting portion) 1a of the laser oscillator 1 is led to the external optical system 4 composed of lenses and others via the total reflection mirror 3 and is irradiated to a workpiece 9 fixed on the table 10 via the optical axis adjusting unit 6 and the condenser lens (fθ lens) 8.
The optical axis adjusting unit 6 is composed of total reflection mirrors 6a and 6b disposed at positions where their axes of rotation are twisted from each other and scanner motors 6c and 6d for turning the total reflection mirrors 6a and 6b. The table 10 is constructed so as to be movable in X and Y directions (in the lateral direction and in the direction perpendicular to the face of the drawing). Thereby, the laser beam 2 may be adjusted to a target position of the workpiece 9 by turning the total reflection mirrors 6a and 6b. It is noted that optically, the optical axis adjusting unit 6 is constructed so as to reduce and form an image that has been formed behind the external optical system 4 at a machining spot by using the condenser lens 8.
By the way, there is a case when the laser beam 2 does not pass through a deflecting point of the condenser lens 8 depending on a turning angle of the total reflection mirror 6a. Due to that, Japanese Patent Laid-Open No. 1993-228673 has proposed one in which a total reflection mirror is disposed between the laser oscillator 1 and the total reflection mirror 6a to adjust an incident position of the laser beam 2 on the total reflection mirror 6a so that the laser beam 2 passes through the deflecting point of the condenser lens 8 by moving the total reflection mirror while keeping the angle thereof with the incident light.
FIG. 6 is a plan view diagrammatically showing the opening 1a of the laser oscillator 1. The optical system composed of lenses and mirrors within the laser oscillator 1 shapes an outline and regulates an angle of divergence of the laser beam 2 formed in an oscillator source within the laser oscillator 1 so that its optical axis coincides with the center Q of the opening 1a of the laser oscillator 1 as shown in FIG. 6 and becomes perpendicular to the opening 1a that is parallel with the face of the drawing. However, because there is a case when the temperature of the lenses and mirrors disposed within the laser oscillator 1 increases, thus causing thermal deformation, when the laser beam passes through them, there is a case when the position of the optical axis in the opening 1a moves to a point Q1 for example deviating from the center Q or when the optical axis is not perpendicular to the opening 1a. Still more, the position of the optical axis in the opening 1a may deviate from the center Q or the optical axis may not become perpendicular to the opening when oscillating frequency or output of the laser oscillator 1 is changed. The deviation from the center Q of the optical axis and its deviating direction as well as an angle of output thereof at the opening 1a also vary depending on use conditions and are not uniform.
The conventional laser machining apparatus described above which is arranged so that the laser beam passes through the deflecting point of the condenser lens 8 by means of the total reflection mirror allows machining to be carried out at high precision as long as the optical axis of the laser beam incident on the total reflection mirror does not vary. However, when the optical axis of the laser beam deviates or its output angle varies, the precision in adjusting the laser beam 2 to the target position drops and hence the precision in machining position drops. Moreover, the image formed behind the external optical system 4 distorts or becomes defective, thus dropping the precision in shape of the spot to be machined.
It is therefore an object of the invention to provide a laser machining apparatus that solves the above-mentioned problems by enabling an optical axis of a laser beam to be adjusted with a predetermined optical axis.